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Statistical bulletin: Super Output Area Population Estimates, Mid-2002 to Mid-2010 (revised)

Released: 26 November 2013 Download PDF

Key points

  • The Super Output Area (SOA) estimates for England and Wales for mid-2002 to mid-2010 have been revised following the 2011 Census. The revised series allows an understanding of how populations in England and Wales have changed across the decade in small areas, illustrated in the case study for Birmingham.
  • The size of the revision is dependent on the size of the difference between the official (census based) mid-2011 estimate for each lower layer SOA (LSOA) and what the mid-2011 LSOA estimates would have been had the 2011 Census results not been available.
  • More than 60% of LSOAs and more than 75% of middle layer SOAs (MSOAs) were revised by less than ±5% across the decade.
  • The largest LSOA revisions were mostly in university areas, with the largest revision in Leeds 055H where the population was overestimated by approximately 2,800 people.
  • Some of the largest MSOA revisions were in Newham local authority which saw an overall upward revision of 68,000 people across the decade.

Summary

This release presents the revised 2002 to 2010 mid-year population estimates for lower layer and middle layer Super Output Areas (LSOA and MSOA respectively) for England and Wales. These estimates correspond to the revised local authority population estimates published on 30 April 2013.

The revised estimates create a consistent series between the mid-2002 and mid-2012 LSOA and MSOA population estimates. They are based on the LSOA and MSOA geographic boundaries published in October 2012 and are broken down by age and sex in order to provide an estimate of the usual resident population as at 30 June each year.

The revised estimates are certified as National Statistics by the UK Statistics Authority.

Introduction

To reflect the 2011 Census results, revised local authority population estimates were published on 30 April 2013. This release provides the corresponding revised lower layer and middle layer Super Output Areas (LSOA and MSOA) estimates for mid-2002 to mid-2010.

The availability of an improved and continuous time series is important as small area population estimates are used by both central government departments and local authorities for a range of purposes including planning and monitoring of services and as denominators for the calculation of various rates and indicators. For further information on the quality and use of these statistics, please see the Quality and Methodology Information for small area population estimates.

What are Super Output Areas?

SOAs were introduced in 2004 to improve the reporting of small area statistics. They are built from groups of census output areas, are of a consistent size and are not subject to boundary changes between censuses. Where possible they are formed from groups of socially similar households and align with local features such as roads and railway lines. The comparability and stability of the geography is a key benefit to users of statistics which cannot be provided by other small area administrative geographies such as wards or parishes.

Following the 2011 Census, some boundary changes to SOAs were required and a new set of SOA boundaries was published in October 2012. However, the stability of the geography has been largely maintained with 97.5% of lower layer SOAs and 97.9% of middle layer SOAs remaining unchanged. For further information please see the full report: ‘ Changes to Output Areas and Super Output Areas in England and Wales, 2001 to 2011’ (287.3 Kb Pdf) . Further information on SOAs, can also be obtained from the geography section of the ONS website.

Two levels of SOAs are available in England and Wales:

  • Lower layer (LSOAs) designed to have a population of between 1,000 and 3,000 in 2011. There are 34,753 LSOAs in England and Wales.

  • Middle layer (MSOAs) designed to have a population of between 5,000 and 15,000 in 2011. There are 7,201 MSOAs in England and Wales. MSOAs are aggregations of LSOAs.

The mid-2002 to mid-2010 population estimates presented in this release are based on the 2011 SOA boundaries.

How have the revised estimates been calculated?

The mid-2002 to mid-2010 estimates are revised in line with the results of the 2011 Census and are consistent with the revised census based local authority estimates. The estimates are updated to account for population change over the intercensal period, to provide a consistent time series for future estimates based on the 2011 Census.

Mid-2011 lower layer Super Output Area (LSOA) census based estimates and mid-2011 ‘rolled forward’ estimates were used to identify differences that may have arisen over the intercensal period. The observed difference in the intercensal period is distributed over time; that is, assuming constant change across the series. A full explanation of the method used to revise these estimates is provided in the methods report.

How much have the estimates changed?

For England and Wales the mid-2011 population estimate, based on the 2011 Census, was 464,200 (0.8%) higher than the ‘rolled forward estimate’ for mid-2011 (that is the estimate originally based on the 2001 Census but updated year-on-year to account for population change).

Difference between mid-2011 census based and mid-2011 ‘rolled forward’ population estimates

Comparisons of the mid-2011 census based lower layer and middle layer Super Output Area (LSOA and MSOA) estimates against rolled forward mid-2011 estimates are presented in this release for all LSOAs and MSOAs. The distribution of the mid-2011 census based LSOA estimates against rolled forward mid-2011 LSOAs and MSOAs are shown in figures 1 and 2 below.

Figure 1: Distribution of percentage difference between rolled forward and census based population estimates for LSOAs, mid-2011

Figure 1: Distribution of percentage difference between rolled forward and census based population estimates for LSOAs, mid-2011
Source: Office for National Statistics

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The rolled forward estimate was within ‡1% of the census based estimate for mid-2011 in 5,339 LSOAs (15.4%) and within ±5% in 22,171 LSOAs (63.8%).More LSOAs were underestimated than overestimated (54.8% compared to 44.8%) as would be expected given the overall underestimation at national level. Less than 1% of LSOAs were unchanged.

Figure 2: Distribution of percentage difference between rolled forward and census based population estimates for MSOAs, mid-2011

Figure 2: Distribution of percentage difference between rolled forward and census based population estimates for MSOAs, mid-2011
Source: Office for National Statistics

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The rolled forward estimate was within ±1% of the census based estimate for mid-2011 in 1,537 MSOAs (21.3%) and within ±5% in 5,521 MSOAs (76.7%). More MSOAs were underestimated than overestimated (58.0% compared to 41.8%).

The top ten LSOAs with the highest levels of overestimation of the total population by the rolled forward series are given in table 1 below. The majority of these areas have high student populations, but also include one area with a high armed forces population – Leeds 055H includes part of the University of Leeds and Forest Heath 002F includes RAF Lakenheath.

Table 1: LSOAs with highest overestimation, mid-2011

Rank LSOA Difference Percentage Difference
1 Leeds 055H 2,800 80.5
2 Forest Heath 002F 2,400 70.0
3 Southampton 029C 2,300 98.3
4 Charnwood 007B 2,100 54.3
5 Cambridge 007G 1,700 33.6
6 Canterbury 012F 1,700 26.9
7 Manchester 026C 1,600 47.4
8 Nottingham 026G 1,600 74.6
9 Cambridge 007F 1,400 40.1
10 Exeter 001F 1,300 25.8

Table source: Office for National Statistics

Table notes:

  1. Figures have been rounded to the nearest 100

  2. The difference is calculated as the rolled forward estimate minus the census based estimate for mid-2011

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The top ten LSOAs with the highest levels of underestimation of the total population by the rolled forward series are shown in table 2 below. These also include areas with high student populations and one area with a high armed forces population – West Oxfordshire 014C which includes part of RAF Brize Norton.

Table 2: LSOAs with highest underestimation, mid-2011

Rank LSOA Difference Percentage Difference
1 Hillingdon 015A 1,500 46.1
2 West Oxfordshire 014C 1,500 49.7
3 Guildford 012A 1,500 49.7
4 Liverpool 060C 1,300 62.9
5 Newham 037A 1,300 46.4
6 Manchester 019C 1,200 38.1
7 Gwynedd 001E 1,200 29.8
8 Welwyn Hatfield 010D 1,200 41.3
9 Wiltshire 041E 1,100 25.4
10 Liverpool 060E 1,100 59.9

Table source: Office for National Statistics

Table notes:

  1. Figures have been rounded to the nearest 100

  2. The difference is calculated as the census based estimate minus the rolled forward estimate for mid-2011

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Change over the decade, mid-2002 to mid-2011

Map 1 shows the percentage growth between the revised mid-2002 and the official mid-2011 MSOA estimates for England and Wales. It also illustrates the different patterns of growth within local authorities in England and Wales. London has a high concentration of MSOAs where the population grew by 5% or more between mid-2002 and mid-2011. Few MSOA areas saw large declines in population over the decade.

Map 1: Percentage population growth by MSOA, mid-2002 to mid-2011, England and Wales

Percentage growth in MSOAs, mid-2002 to mid-2011

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Case Study: How much have the estimates changed in Birmingham local authority?

The following case study considers the different patterns of population growth for Super Output Areas (SOAs) in Birmingham between mid-2002 and mid-2010.

Birmingham is a unitary authority located in the West Midlands. Under the ONS urban/rural classification Birmingham is classified as Major Urban which is defined as ‘districts with either 100,000 people or 50 per cent of their population in urban areas with a population of more than 750,000’. Birmingham contains four universities (Aston, Birmingham City, University College Birmingham and the University of Birmingham), a prison (HMP Birmingham) and one boarding school.

In mid-2002 its population was 990,400 (revised), but by the census based mid-2011 estimate it had risen by 83,900 to 1,074,300. The rolled forward mid-2011 estimate gave a different picture. This suggested that Birmingham’s population was 1,047,100 - 27,200 lower than the mid-2011 census based estimate.

Map 2 below shows how this difference between the mid-2011 census based and rolled forward estimate has been distributed across lower layer Super Output Areas (LSOAs) within Birmingham local authority. It is noticeable that LSOAs in Birmingham were more likely to be underestimated than overestimated. 404 LSOAs (63.2%) were underestimated by more than 1%, whereas 202 LSOAs (31.6%) were overestimated by 1%.

Map 2: Percentage difference between census based and rolled forward LSOA estimates, mid-2011, Birmingham

Percentage difference between census based and rolled forward LSOA estimates, mid-2011, Birmingham

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Map 3 shows the percentage growth between the revised mid-2002 and mid-2011 census based LSOA estimates in Birmingham local authority. Approximately half of LSOAs (51.2%) saw population growth of 5% or more between mid-2002 and mid-2011.

Map 3: Percentage population growth by LSOA, mid-2002 to mid-2011, Birmingham

Percentage population growth by LSOA, mid-2002 to mid-2011, Birmingham

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    (261.9 Kb)

The median age for middle layer Super Output Areas (MSOAs) within Birmingham local authority varied widely between different areas. In mid-2002 the lowest median age in an MSOA was 22.4 in Birmingham 096. This MSOA also had the lowest median age in mid-2011 (21.6). Notably the University of Birmingham is very close to this MSOA. Birmingham 004A had the highest median age in mid-2002 (47.3) and the second highest median age in mid-2011 (48.3). This MSOA is located in a residential area within the town of Sutton Coldfield.

Map 4 below highlights how median age changed in MSOAs between mid-2002 and mid-2011. Median age in Birmingham 042 was 31.7 in mid-2011, a decrease of 8.0 years since mid-2002. The median age in Birmingham 012 was 44.4 in mid-2011, an increase of 4.2 years since mid-2002.

Map 4: Change in median age by MSOA, mid-2002 to mid-2011, Birmingham

Change in median age by MSOA, mid-2002 to mid-2011, Birmingham

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Small area population estimates for other UK countries

Population estimates are produced for similar small areas in both Scotland and Northern Ireland, however they are not produced using the same methodology as for Super Output Areas (SOAs)  in England and Wales.

National Records of Scotland (NRS) produce population estimates for Scottish data zones, which are slightly smaller areas than lower layer SOAs designed to contain approximately 500 to 1,000 household residents. NRS use a cohort component based method to produce estimates for data zones, further information on this methodology and the latest estimates (for mid-2011 based on 2001 Census results) are available from their website. Mid-2011 and mid-2012 small area estimates (based on 2011 Census results) are planned for publication by the end of 2013.

The Northern Ireland Statistics and Research Agency (NISRA) publish population estimates for Super Output Areas in Northern Ireland. These are of similar size to English and Welsh lower layer SOAs with populations of approximately 1,300 to 2,800 with a target size of 2,000. NISRA use a mixed methodology based on both cohort component and ratio change approaches. Further information and the latest estimates published for mid-2010 are available from the NISRA website. Estimates for mid-2011 and mid-2012 are currently planned for publication during winter 2013/2014. Revised small area population estimates for the period mid-2001 to mid-2010, to take account of the 2011 Census results, are also planned for winter 2013/2014.

A paper, Small Area Population Estimates across the UK which provides a broad description of the different methodologies used to produce small area population estimates in each constituent country of the UK, is also available on the NISRA website.

Other Publications on Population Estimates

ONS produce statistics on the size, structure and geographic distribution of the population, on the factors driving population change (births, deaths and migration) and on topics such families and older people. In addition to the main national and local authority mid-year population estimates and the Super Output Area (SOA) estimates, other population estimates are produced. These include:

  • parliamentary constituencies

  • wards

  • health geographies

  • the very elderly

In addition, detailed results from the 2011 Census provide information on the characteristics, for example, country of birth or marital status for small areas.

An Overview of Population Statistics is available on the ONS website.

Background notes

  1. National Statistics are produced to high professional standards set out in the Code of Practice for Official Statistics. They undergo regular quality assurance reviews to ensure that they meet customer needs. They are produced free from any political interference.

  2. Published tables include population estimates for middle layer Super Output Areas (MSOAs) and lower layer Super Output Areas (LSOAs) by single year of age and sex. These tables are unformatted to enable re-use of the data. Mid-2011 population estimates have been included in the reference tables to provide a complete and consistent series. Note that the mid-2011 estimates have not been revised as part of this release and there are no plans to revise them. Mid-2011 population estimates for Super Output Areas (SOAs) were published on 11 April 2013.

  3. A report describing the methodology used to create the SOA estimates is available on the ONS website.

  4. This is the fourth release of the mid-2002 to mid-2004 population estimates for SOAs in England and Wales; the third release of the mid-2005 to mid-2008 population estimates; and the second release of the mid-2009 to mid-2010 population estimates.

  5. No pre-release access requests were made for these estimates.

  6. Revised mid-2002 to mid-2010 subnational population estimates are also available on the ONS website.

  7. Mid-2011 and mid-2012 SOA population estimates are also available on the ONS website.

  8. An Overview of Population Statistics is available on the ONS website.

  9. Release Number: SAPE8BL1

  10. Issued by:
    Office for National Statistics, Government Buildings, Cardiff Road, Newport NP10 8XG

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  11. © Crown copyright 2013.
    You may re-use this information (not including logos) free of charge in any format or medium, under the terms of the Open Government Licence or write to the Information Policy Team, The National Archives, Kew, London TW9 4DU
    Email:  psi@nationalarchives.gsi.gov.uk

  12. Details of the policy governing the release of new data are available by visiting www.statisticsauthority.gov.uk/assessment/code-of-practice/index.html or from the Media Relations Office email: media.relations@ons.gsi.gov.uk

    These National Statistics are produced to high professional standards and released according to the arrangements approved by the UK Statistics Authority.

Statistical contacts

Name Phone Department Email
Pete Large +44 (0)1329 444664 Population Estimates Unit sape@ons.gsi.gov.uk
Get all the tables for this publication in the data section of this publication .
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